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A composition of a student of mine:
As I don't usually pay attention to the fact that I breathe, so I have not been aware of the importance of my family: they are always there.


What he's supposed to write is something like "To me, my family has been like the air we breathe; I haven't been conscious of their importance because they are always there."

Does the usage of "As...so..." in his sentence make sense? Does it sound natural to you native speakers?
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IT sounds ok but a little ambiguous when written. In speech you would make the meaning clear.

'...so I have also not been aware...' clarifies things.
Comments  
I agree with Nona's comment that it would have to be a little looser in speech.

I would associate this formation ('as is X, so is Y') with extended similes in verse:

'As an unperfect actor on the stage,
Who with his fear is put besides his part,
Or some fierce thing replete with too much rage,
Whose strength's abundance weakens his own heart;
So I, for fear of trust, forget to say
The perfect ceremony of love's rite...' (Shakespeare, Sonnet ***)

'Family environment = air' seems a just comparison. But:

'I breathe' – I am the active party.
'Someone else is important to me' – I am the ?passive party.

Interesting.

MrP